The invention concerns array antennas and especially broadband (5 to 10%) array antennas for aerospace applications in particular. These array antennas comprise many elements and their feed arrangements which are adapted to confer upon the radiated field the shape required for the specific intended application. There is therefore a requirement for an element that is cheap to manufacture (because large numbers are required, possibly up to several thousand), which are neither heavy nor bulky (because of the aerospace implications) and which are easy to integrate into the antenna (layout and feed geometry). Moreover, in new antenna designs there is the requirement to be able to dispose these elements on a conformed or possibly deformable surface.
In the field of satellite communications it is standard practice to use narrow or spot beams. This means that the main lobes of the radiated fields of the beam are relatively narrow and that beams of this type have a fairly small footprint on the ground. However, the main lobe can be formed in various ways, to create elongate or asymmetric footprints, for example. The requirement is usually to match the footprint on the ground to the geographical coverage area so that power is not wasted by radiating it unnecessarily outside this area. A lobe of an array antenna beam is formed by the geometry or the relative arrangement of the antenna elements and by the amplitude and the phase of the excitation signals applied to the elements by a feed array and its control electronics.
In the practical manufacture of array antennas several elements are often grouped together in subsystems which have a common control point in the amplitude and phase control system. FIG. 1 shows one example of a printed circuit feed array for four printed circuit antenna elements. An antenna element of this type is usually referred to as a "patch". Failing a monolithic global implementation, a subsystem may be constructed purely mechanically, forming the basic building block of a modular antenna structure, which facilitates maintenance and repair.
Printed circuit or plane array antennas made up an antenna elements have been known for at least 15 years and are used in increasingly varied application areas. Many patent and other publications define the state of the art in this field. Some of the better known references are listed below, and are hereby incorporated into this application as a description of the prior art:
1) MICROSTRIP ANTENNA TECHNOLOGY, K. Carver, J. W Mink, IEEE. AP vol AP 29.--N.degree. 1 Jan. 1981. PA1 2) ANNULAR SLOT ANTENNA WITH A STRIPLINE FEED, M. FASSET, 23 Jun. 1989--U.S. Patent. PA1 3) A NEW BROADBAND STACKED TWO LAYER MICROSTRIP ANTENNA--A. Sabban--APS 1983--P63-66 IEEE. PA1 4) ANTENNE PLANE (PLANE ANTENNA)--T. Dusseux, M. Gomez-HENRI, G. RAGUENET--French Patent N.degree. 89 11829, 11 September 1989--Publ. FR 2 651 926.
These printed circuit array antenna systems are thus well known in their simple or multiresonator versions. Their main advantages, as compared with older array antennas made up of horn or helix type elements, are their compact size and low weight. Their great mechanical strength is also relevant in aerospace applications. On the other hand, the bandwidth of patch type elements is relatively small, up to around only a few percent in the simplest version.